Former Prince George's County Executive Jack Johnson, accused in a widespread probe into pay-to-play business dealings, pleaded guilty Tuesday to federal charges of extortion and witness and evidence tampering.

The plea comes six months after authorities say Johnson was overheard in a telephone conversation recorded by the FBI directing his wife to flush down the toilet a $100,000 check from a developer and to conceal nearly $80,000 in cash in her underwear.

"I'm very sorry for what happened," Johnson said outside court. "We all have sinned and fallen short of the glory of the lord."

Johnson, 61, could have faced decades in prison if convicted at trial of all charges -- extortion, bribery, conspiracy and witness and evidence tampering. Sentencing is set for Sept. 15.

Johnson was arrested in November, along with his wife, Leslie Johnson.

Leslie Johnson was elected to the County Council shortly before her arrest and was sworn in despite calls from several council members that she step aside. She was scheduled to enter a guilty plea earlier this month, but the hearing was abruptly canceled. Any felony conviction would force her to give up her office.

Jack Johnson, a Democrat, led the county of more than 860,000 people from 2002-2010 and was arrested with less than a month left in his term. Prince George's is the nation's wealthiest majority-black jurisdiction, but it has long been plagued by crime, corruption and failing schools.

He was indicted in February on charges of extortion, bribery, witness and evidence tampering and conspiracy. Prosecutors accused him of accepting more than $200,000 in cash, campaign contributions and other gifts to help developers. He would have faced decades in prison if convicted of all charges at trial.

The FBI tapped Johnson's phones for nearly a year, and prosecutors released detailed transcripts of colorful telephone conversations between Johnson and his alleged co-conspirators.

The highlight was a frantic Johnson instructing his wife to flush the check from a developer down the toilet and hide cash in her underwear as FBI agents knocked on the door of their Mitchellville home.

"Do you want me to put it down the toilet?" Leslie Johnson asked her husband, according to the documents.

"Yes, flush that," Johnson said.

He then instructed his wife to hide $79,600 in her bra and underwear, where FBI agents found it after searching her, the documents show.